Obstructive sleep apnea syndrome (OSAS) is a frequent condition affecting up to 5 percent of the population, and is characterized by repeated episodes of hypoxia and recurrent EEG/behavioral arousal, particularly during REM sleep. When untreated, OSAS is associated with significant neurocognitive morbidities such as excessive daytime sleepiness and diminished intellectual performance, attention span, learning and vigilance. However, the relative contributions of REM sleep deprivation (REMSD) and episodic hypoxia to OSAS-associated neurocognitive dysfunction remain unclear. To test the hypothesis that REM sleep deprivation and episodic hypoxia affect learning and memory in an additive fashion, four major specific aims will be examined in a young adult rat model as follows: (1) The acquisition and retention of Morris water maze task paradigms will be assessed in conscious 55-60-day old male rats after either 4-day REMSD using the inverted flower pot technique, 14-day episodic daytime hypoxia (EHYP), or the combination thereof (REMSD-EHYP); (2) The effect of such exposure paradigms on long-term potentiation (LTP) within the CA1 region of the hippocampus will be examined using neurophysiological extracellular recordings of the in vitro hippocampal slice preparation; (3) Changes in ionotropic glutamate receptor distribution and in apoptosis within the hippocampal formation and neocortex will be determined using immunohistochemical and wester blot approaches in naive and maze trained animals following REMSD, EHYP, or both; (4) Alterations in early gene induction (c-fos) elicited by maze learning procedures will be further assessed in the hippocampus of REMSD, EHYP, and REMSD-EHYP by immunohistochemistry and AP-1 electromobility shift assays. These e xperiments will extend our understanding on potential mechanisms and interactions underlying the decreased performance that occurs in particular neurocognitive functions of untreated OSAS patients. In this context, REMSD, EHYP, or both would lead to either up-regulation or down-regulation of specific ionotropic glutamate receptor complexes, induce apoptosis, and thereby modify early gene activation patterns associated with learning or retention of newly learned tasks. Such alterations in receptor-signal transduction pathways could also lead to both short- and long- term changes in neuronal excitability and synaptic transmission within brain regions with important and defined roles in memory formation and learning such as the hippocampus.